Redefining prostate cancer risk stratification: a pioneering strategy to estimate outcome based on Ki67 immunoscoring

Accurate prostate cancer (PCa) patient diagnosis and risk assessment are key to ensure the best outcome. Currently, low- and favorable intermediate-risk PCa patients may be offered AS due to the indolent nature of the disease. Nonetheless, deciding between active surveillance and curative-intent treatment remains an intricate task, as a subset of these patients may eventually progress, enduring poorer prognosis. Herein, we sought to construct risk calculators based on cancer biomarkers, enabling more accurate discrimination among patients which may benefit from active interventions. Ki67 immunoscore, GSTP1 and KLF8 promoter methylation levels (me) were assessed in PCa tissues. Study endpoints included overall and biochemical recurrence-free (BCR) survival. Combination with relevant clinicopathological parameters allowed for construction of graphical calculating tools (nomograms). Higher Ki67 index correlated with worse BCR-free survival, whereas higher KLF8me levels were associated with improved overall survival, especially in patients with lower-grade tumors. GSTP1me levels had no prognostic value. Among prognostic models tested, a BCR-risk calculator – ProstARK (including Ki67 and clinicopathologic parameters) – disclosed 79.17% specificity, 66.67% sensitivity, 55% positive predictive value, 86% negative predictive value, and 75.76% accuracy. Similar results were found using an independent PCa biopsy cohort, validating its prognostication ability. Combining clinicopathologic features and Ki67 index into a risk calculator enables easy and accurate implementation of a novel PCa prognostication tool. This nomogram may be useful for a more accurate selection of patients for active surveillance protocols. Nonetheless, validation in a larger, multicentric, set of diagnostic PCa biopsies is mandatory for further confirmation of these results. Supplementary Information The online version contains supplementary material available at 10.1186/s40364-024-00627-4.

To the editor, Accurate prostate cancer (PCa) risk assessment is key to ensure the best outcome.Nearly 90% of PCa are diagnosed as organ-confined [1] making clinical decisions on the best therapeutic strategy challenging [2,3].For lowand favorable intermediate-risk PCa-grade group (GG) 1 and 2-active surveillance (AS) is frequently considered [2], although this is not risk-exempt considering that some patients ultimately experience disease progression [4].Currently, patients in AS are monitored through frequent biopsies, without uniform guidelines, and are proposed for active treatment only when increased tumor grade or stage is detected [4,5].Because accurate prognostic biomarkers may assist clinicians in deciding the best strategy, we sought to investigate whether molecular [GSTP1 and KLF8 promoter hypermethylation ( me )] and/ or immunohistochemical (Ki67 immunoscore) biomarkers might discriminate among patients with low or highrisk of PCa progression, using prostatectomy-derived tissues with subsequent validation in diagnostic biopsies.Ki67 index is a marker of aggressiveness/recurrence in several cancers [6], however, in PCa is not yet the standard care [7].DNA methylation-based biomarkers, like GSTP1 me and KLF8 me hold promise for cancer detection and prognostication [1], although KLF8 me needs further exploration [1,8].
Although we and others have shown the value of GST-P1 me for PCa detection [8], its prognostic performance was rather limited in this study, only significantly differing between stage III and stage II PCa patients (supplementary figure S1A).KLF8 me levels significantly differed between higher and lower tumor stages and low KLF8 me and significantly associated with worse overall survival (OS) in GG1/2 PCa patients (Supplementary Figure S1B  and S2A).Nonetheless, this has limited clinical significance because OS is mostly influenced by age.
Confirming Ki67 immunoscore as a promising PCa prognostic biomarker [9,10], we found that it correlated with higher stage and GG, demonstrating the association between proliferation and tumor aggressiveness (Supplementary Figure S1C/D).Importantly, high Ki67 immunoscore significantly associated with shorter biochemical recurrence (BCR)-free survival (a surrogate for metastatic disease and mortality), but not with OS (data not shown), recapitulating similar findings in other tumor models [11].Specifically, Ki67 score 2 and 3 PCa patients endured significantly lower BCR-free survival, both globally and considering GG1/2 patients only, respectively (Supplementary Figure S2B/C).
Importantly, ProstARK high NPV suggests that it may assist in more accurately identifying patients benefiting from AS.It is tempting to speculate whether, in this scenario, ProstARK may better discriminate patients at risk for progression, despite unchanged grade or stage, to which active therapy might be offered.This may allow a reduction of subsequent, needless, biopsies with the refinement of the follow-up strategies for patients at higher risk for recurrence/progression.
Other genomic tests are currently available with the same purpose.Although Decipher ® predicts adverse pathology (AUC = 0.65), it is less effective for AS [12].Oncotype DX ® has similar limitations (AUC = 0.68) [12], whereas Prolaris ® predicts recurrence (AUC = 0.825), but at high cost [12].ProstARK is cost-effective and accessible, unlike genomic tests, and leverages widely available equipment and know-how in pathology labs.Eventually, with the rise of Digital Pathology, Ki67 scoring may be further perfected.
In conclusion, the combination of clinicopathologic parameters and Ki67 into a risk calculator enables easy and accurate implementation of a novel PCa prognostication tool.A multicentric validation study using diagnostic PCa biopsies is planned and may include additional promising biomarkers.

Fig. 2
Fig. 2 Risk Calculators evaluation in the Discovery and Validation Cohorts GG1/2.A Kaplan-Meier curve for overall survival based on the risk of death calculator, in the Discovery Cohort GG1/2.A -0.37 cut-off for the linear predictor translates into risk of death of 0.41.B Kaplan-Meier curves for the biochemical-recurrence free survival based on the ProstARK calculator, in Discovery Cohort GG1/2.A -0.82 cut-off for the linear predictor translates into recurrence/progression risk of 0.31.C ROC curve to evaluate the performance of the ProstARK, in Validation Cohort GG1/2 patients.D Kaplan-Meier curve for the biochemical-recurrence free survival based on the ProstARK calculator, in Validation Cohort GG1/2 patients.A -0.82 cut-off for the linear predictor translates into recurrence/progression risk of 0.31 in D)